1. Technical Field
The present invention relates to a lithium battery and, more particularly, to a polymer electrolyte composition for improving overcharge safety, and a lithium battery using the same.
2. Related Art
According to the development of advanced electronic devices, there is an increasing demand for small, lightweight portable electronic devices and equipment. Thus, there is a need for batteries having high energy density characteristics so as to supply power to such devices and equipment.
A lithium battery comprises a cathode, an anode, an electrolytic solution providing a movement path for lithium ions, and a separator disposed between the cathode and the anode. Lithium batteries produce electrical energy by intercalation/deintercalation of lithium ions during oxidation and reduction occurring at the cathode and the anode. However, in the case where a battery is overcharged due to malfunction of a charger (for example, malfunction causing a sharp rise in voltage), excess lithium is precipitated at the cathode and excess lithium is intercalated into the anode. If both the cathode and the anode are thermally unstable, an organic solvent of the electrolytic solution is decomposed to cause rapid heat generation, such as thermal runaway, adversely affecting safety of the battery.
To overcome the foregoing disadvantage, various attempts to suppress overcharge of a battery by changing the composition of an electrolytic solution or adding additives to the electrolytic solution have been proposed in the field of lithium ion batteries. For example, U.S. Pat. No. 5,580,684 to Yokoyama et al., entitled NON-AQUEOUS ELECTROLYTIC SOLUTIONS AND NON-AQUEOUS ELECTROLYTE CELLS COMPRISING THE SAME, issued on 3 Dec. 1996, discloses a method of improving safety of a battery by increasing a self-extinguishing property of an electrolytic solution by adding phosphoric acid esters, such as trimethyl phosphate, tri(trifluoroethyl)phosphate or tri(2-chloroethyl)phosphate, to the electrolytic solution. U.S. Pat. No. 5,776,627 to Mao et al., entitled AROMATIC MONOMER GASSING AGENTS FOR PROTECTING NON-AQUEOUS LITHIUM BATTERIES AGAINST OVERCHARGE, issued on 7 Jul. 1998, discloses a lithium battery having an internal electrical disconnection device, and comprising a gas generating additive, such as thiophene, biphenyl or furan. When the battery is overcharged, the gas generating additive is polymerized to prevent migration of lithium ions, and the generated gas increases an internal pressure of the battery so that the disconnection device is activated, thereby causing internal shorting prior to explosion.
Similarly, methods for enhancing battery safety are disclosed in U.S. Pat. No. 5,763,119 to Adachi, entitled NON-AQUEOUS ELECTROLYTE SECONDARY CELL HAVING SHUTTLE AGENT, issued on 9 Jun. 1998, U.S. Pat. No. 5,709,968 to Shimizu, entitled NON-AQUEOUS ELECTROLYTE SECONDARY BATTERY, issued on 20 Jan. 1998, and U.S. Pat. No. 5,858,573 to Abraham et al., entitled CHEMICAL OVERCHARGE PROTECTION OF LITHIUM AND LITHIUM-ION SECONDARY BATTERIES, issued on 12 Jan. 1999, in which an electrolyte includes an additive such as 1,2-dimethoxy-4-bromo-benzene, 2-chloro-p-xyline and 4-chloro-anisol, and 2,7-diacetyl thianthrene, respectively.
However, such conventional additives may be polymerized even under normal operating conditions. Also, since additional disconnections are necessary, resultant batteries become bulky. In the case of a lithium polymer battery requiring a large amount of additives, life cycle characteristics may deteriorate.